Many commercial processes use high purity gas from the tanks or cylinders of compressed or liquefied gas. For example, the electronics industry requires high purity gases and gas mixtures which are substantially free from other compounds that serve as impurities and contaminate the gas for its intended use. High purity gases and gas mixtures containing less than a total of 50 parts per million (ppm) nitrogen, oxygen, carbon monoxide, carbon dioxide, hydrocarbons and water are routinely required. More demanding purity applications decrease contaminants to less than a few parts per million of a specific impurity, for example water. More recently, even more stringent specifications have been set down requiring impurity concentration of less than several parts per billion.
Ordinarily tanks or cylinders can not directly supply gas of sufficient purity for such processes. Even special preparation of the cylinders by polishing and baking the inner surfaces still fails to produce sufficient purity. Therefore, purifiers at the point of use are commonly employed to remove contaminants and raise the purity of the gas as it is delivered.
U.S. Pat. No. 1,821,549 establishes the long known use of in-tank purifiers to remove contaminants from compressed gases or liquefied gases delivered by high pressure cylinders. Economical cylinder design results in a single opening for filling and delivery of gases from the cylinder. Filling the gases and removing purified gases from the same opening has presented persistent problems. Filling the cylinder by passing gas through a purifier located therein loads the outlet region of the purifier with contaminants that can reenter the gas stream delivered by the cylinder. U.S. Pat. No. 5,409,526 discloses an apparatus arrangement for filling a cylinder with a gas through one port defined in a cylinder head and discharging gas through another port into which a purifier supplies exiting gas. While U.S. Pat. No. 5,409,526 solves problems related to the contaminating the purifier with incoming gas, the need to provide two separate ports through the limited cross section of the cylinder head impedes rapid filling of the cylinder with gas.
It is an object of this invention to provide an apparatus that facilitates filling of tanks or cylinders as well as purification of delivered gas as it exits a cylinder or tank.
It is an additional object of this invention to provide an apparatus that indicates the operating state of an in-tank purifier.
It is a further object of this invention to provide an arrangement that will simplify by-passing of a purifier to rapidly evacuate gases from a cylinder or tank.